The birthplace of the Islamic State (ISIS) has been traced to Camp Bucca, a detention center that was operated by the United States military during the Iraq war.

According to The Washington Post, many ISIS leaders, including Abu Bakr al-Baghdadi, “were incarcerated and probably met” at Camp Bucca, “which had detained some of the war’s most radical extremists along the Kuwait border.” “According to former prison commanders, analysts and soldiers, Camp Bucca provided a unique setting for both prisoner radicalization and inmate collaboration — and was formative in the development of today’s most potent jihadist force,” reports the Post. Citing the terrorism research firm Soufan Group, the outlet mentions that a total of nine members of ISIS leadership were once detained at Bucca, located in the southern Iraqi town of Garma.

“Apart from Baghdadi himself, who spent five years there, his deputy, Abu Muslim al-Turkmani, as well as senior military leader Haji Bakr, now deceased, and the leader of foreign fighters, Abu Qasim, were incarcerated there, Soufan said,” according to the Post. “Though it’s likely that the men were extremists when they entered Bucca, the group added, it’s certain they were when they left.”

The Washington Post links the beginning of ISIS to the March 2009 release of hundreds of inmates from Bucca. Police Chief Saad Abbas Mahmoud told the Post that around 90 percent of the freed prisoners would return to the battlefield. Reports the newspaper, “Mahmoud’s assessment of Camp Bucca, which funneled 100,000 detainees through its barracks and closed months later, would prove prescient,” and “the camp now represents an opening chapter in the history of the Islamic State.”

“From the ashes of what former inmates called an ‘al-Qaeda school’ rose the Islamic State,” asserts the article.